drm/fb-helper: Fix typo on kerneldoc

Copypasta mistake.

Fixes: 742547b73d27 ("drm/fb_helper: Create wrappers for blit, copyarea and fillrect funcs")
Cc: Archit Taneja <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Gustavo Padovan <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Sean Paul <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: [e-mail]
Acked-by: Noralf Trønnes <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_fb_helper.c

···
  * @info: fbdev registered by the helper
  * @rect: info about rectangle to fill
  *
- * A wrapper around cfb_imageblit implemented by fbdev core
+ * A wrapper around cfb_fillrect implemented by fbdev core
  */
 void drm_fb_helper_cfb_fillrect(struct fb_info *info,
 				const struct fb_fillrect *rect)